netdev - Re: [PATCH net-next] tcp: be less liberal in tsecr received while in SYN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iLH_SgpWgAXvDjRbpFtVjWS-yLSiX0FbCweWjAJgzaASg@mail.gmail.com>
Date: Tue, 25 Feb 2025 11:37:53 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Simon Horman <horms@...nel.org>, Florian Westphal <fw@...len.de>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Jakub Kicinski <kuba@...nel.org>, 
	Yong-Hao Zou <yonghaoz1994@...il.com>, "David S . Miller" <davem@...emloft.net>, 
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: be less liberal in tsecr received while in
 SYN_RECV state

On Tue, Feb 25, 2025 at 11:33 AM Matthieu Baerts <matttbe@...nel.org> wrote:
>
> On 25/02/2025 11:21, Eric Dumazet wrote:
> > On Tue, Feb 25, 2025 at 11:19 AM Matthieu Baerts <matttbe@...nel.org> wrote:
> >>
> >> Hi Eric,
> >>
> >> On 25/02/2025 11:11, Eric Dumazet wrote:
> >>> On Tue, Feb 25, 2025 at 11:09 AM Matthieu Baerts <matttbe@...nel.org> wrote:
> >>>>
> >>>> Hi Paolo, Eric,
> >>>>
> >>>> On 25/02/2025 10:59, Paolo Abeni wrote:
> >>>>> On 2/24/25 12:06 PM, Eric Dumazet wrote:
> >>>>>> Yong-Hao Zou mentioned that linux was not strict as other OS in 3WHS,
> >>>>>> for flows using TCP TS option (RFC 7323)
> >>>>>>
> >>>>>> As hinted by an old comment in tcp_check_req(),
> >>>>>> we can check the TSecr value in the incoming packet corresponds
> >>>>>> to one of the SYNACK TSval values we have sent.
> >>>>>>
> >>>>>> In this patch, I record the oldest and most recent values
> >>>>>> that SYNACK packets have used.
> >>>>>>
> >>>>>> Send a challenge ACK if we receive a TSecr outside
> >>>>>> of this range, and increase a new SNMP counter.
> >>>>>>
> >>>>>> nstat -az | grep TcpExtTSECR_Rejected
> >>>>>> TcpExtTSECR_Rejected            0                  0.0
> >>>>
> >>>> (...)
> >>>>
> >>>>> It looks like this change causes mptcp self-test failures:
> >>>>>
> >>>>> https://netdev-3.bots.linux.dev/vmksft-mptcp/results/6642/1-mptcp-join-sh/stdout
> >>>>>
> >>>>> ipv6 subflows creation fails due to the added check:
> >>>>>
> >>>>> # TcpExtTSECR_Rejected            3                  0.0
> >>>>
> >>>> You have been faster to report the issue :-)
> >>>>
> >>>>> (for unknown reasons the ipv4 variant of the test is successful)
> >>>>
> >>>> Please note that it is not the first time the MPTCP test suite caught
> >>>> issues with the IPv6 stack. It is likely possible the IPv6 stack is less
> >>>> covered than the v4 one in the net selftests. (Even if I guess here the
> >>>> issue is only on MPTCP side.)
> >>>
> >>>
> >>> subflow_prep_synack() does :
> >>>
> >>>  /* clear tstamp_ok, as needed depending on cookie */
> >>> if (foc && foc->len > -1)
> >>>      ireq->tstamp_ok = 0;
> >>>
> >>> I will double check fastopen code then.
> >>
> >> Fastopen is not used in the failing tests. To be honest, it is not clear
> >> to me why only the two tests I mentioned are failing, they are many
> >> other tests using IPv6 in the MP_JOIN.
> >
> > Yet, clearing tstamp_ok might be key here.
> >
> > Apparently tcp_check_req() can get a non zero tmp_opt.rcv_tsecr even
> > if tstamp_ok has been cleared at SYNACK generation.
>
> Good point. But in the tests, it is not suppose to clear the timestamps.
>
> (Of course, when I take a capture, I cannot reproduce the issue :) )
>
> >
> > I would test :
> >
> > diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> > index a87ab5c693b524aa6a324afe5bf5ff0498e528cc..0ed27f5c923edafdf48919600491eb1cb50bc913
> > 100644
> > --- a/net/ipv4/tcp_minisocks.c
> > +++ b/net/ipv4/tcp_minisocks.c
> > @@ -674,7 +674,8 @@ struct sock *tcp_check_req(struct sock *sk, struct
> > sk_buff *skb,
> >                 if (tmp_opt.saw_tstamp) {
> >                         tmp_opt.ts_recent = READ_ONCE(req->ts_recent);
> >                         if (tmp_opt.rcv_tsecr) {
> > -                               tsecr_reject = !between(tmp_opt.rcv_tsecr,
> > +                               if (inet_rsk(req)->tstamp_ok)
> > +                                       tsecr_reject =
> > !between(tmp_opt.rcv_tsecr,
> >
> > tcp_rsk(req)->snt_tsval_first,
> >
> > READ_ONCE(tcp_rsk(req)->snt_tsval_last));
> >                                 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
> Thank you for the suggestion. It doesn't look to be that, I can still
> reproduce the issue.
>
> If I print the different TS (rcv, snt first, snt last) when tsecr_reject
> is set, I get this:
>
> [  227.984292] mattt: 2776726299 2776727335 2776727335
> [  227.984684] mattt: 2776726299 2776727335 2776727335
> [  227.984771] mattt: 3603918977 3603920020 3603920020
> [  227.984896] mattt: 3603918977 3603920020 3603920020
> [  230.031921] mattt: 3603918977 3603920020 3603922068
> [  230.032283] mattt: 2776726299 2776727335 2776729383
> [  230.032554] mattt: 2776729384 2776727335 2776729383
>       ack rx                [FAIL] got 0 JOIN[s] ack rx expected 2

req->num_timeout might not be updated where I thought it was.